Method for optimum mounting of piezoelectric ceramic filter elements

ABSTRACT

AN APPARATUS AND METHOD OF MOUNTING A PIEZOELECTRIC CERAMIC ELEMENT TO PROVIDE OPTIMUM ELECTRICAL/MECHANICAL FUNCTIONING, THE APPARATUS INCLUDING A RECEPTACLE HAVING A FIXED CONTACT AND A MOVABLE CONTACT BETWEEN WHICH THE CERAMIC ELEMENT IS CLAMPED, THE CLAMPING FORCE BEING VARIABLE VIA THE MOVABLE CONTACT, WHICH IN ONE FORM IS A SLEEVE WITH A RESILIENT COUPLED PLUNGER, SLIDABLY ADJUSTABLE IN THE SLEEVE AND BEARING AGAINST THE ELEMENT.   THE METHOD OF MOUNTING THE ELEMENT CONSISTS OF PROVIDING A CIRCUIT ACROSS THE AFORESAID CONTACTS INCLUDING A VARIABLE FREQUENCY, ALTERNATING CURRENT SOURCE SET TO THE OPERATING, OR RESONANT, FREQUENCY OF THE ELEMENT AND A MILLIAMMETER, VARYING THE MOVABLE CONTACT TO CHANGE THE CLAMPING FORCE, AND FIXING THE MOVABLE CONTACT FROM FURTHER VARIATION WHEN A MAXIMUM DEFLECTION OF THE MILLIAMMETER IS OBTAINED.

NOV. 23, 1971 3,621,547

METHOD FOR OPTIMUM MOUNTING OF PIEZOELECTRIC C. T. DURHAM. JR

CERAMIC FILTER ELEMENTS Filed May 16, 1969 x ,///A//// /W I a INVEN'I'OR. CARL '1. DURHAM, JR.

United States Patent 3,621,547 METHOD FOR OPTIMUM MOUNTING OF PIEZO- ELECTRIC CERAMIC FILTER ELEMENTS Carl T. Durham, Jr., Roanoke, Va., assignor to General Electric Company Filed May 16, 1969, Ser. No. 825,279 Int. Cl. B01j 17/00 US. Cl. 2925.35 4 Claims ABSTRACT OF THE DISCLOSURE An apparatus and method of mounting a piezoelectric ceramic element to provie optimum electrical/mechanical functioning, the apparatus including a receptacle having a fixed contact and a movable contact between which the ceramic element is clamped, the clamping force being variable via the movable contact, which in one form is a sleeve with a resiliently coupled plunger, slidably adjustable in the sleeve and bearing against the element.

The method of mounting the element consists of providing a circuit across the aforesaid contacts including a variable frequency, alternating current source set to the operating, or resonant, frequency of the element and a milliammeter, varying the movable contact to change the clamping force, and fixing the movable contact from further variation when a maximum deflection of the milliammeter is obtained.

BACKGROUND OF THE INVENTION Piezoelectric crystals and ceramic elements normally are mounted for use as filters, oscillators and the like between two contacts resiliently bearing upon opposite surfaces of the crystal or element, the surfaces normally being coated with a conductive material and the contacts being urged against the coatings. Normally no effort is made to adjust the contact tension against these surfaces other than to make electrical contact. It has been demonstrated, however, that the contact pressure against these surfaces is somewhat critical.

SUMMARY OF THE INVENTION The present invention is directed to providing a mounting for piezoelectric elements wherein optimum functional performance, both electrically and mechanically, is obtained by securing the piezoelectric element between contacts whose contact pressure is adjusted in accordance with the critical, operating, or resonant, frequency of the element when it is actually functioning in a circuit energized with electromotive force of the aforesaid frequency to give a maximum current in the circuit.

DESCRIPTION The drawing is a sectional view showing a mounting apparatus 11 for a piezoelectric ceramic element 13, preferably provided with a conductive coating 16 on its two major surfaces which is clamped between a stationary contact 15 and a movable contact 17. The contact 15 projects internally and axially from a bottom plate 19 of an enclosure 21 to support one side of element 13, and the movable contact 17 contacts the other side of element 13 via a spring 23 attached to one end of a rod 25.

Rod 25 is slidably fitted in a metallic tube 27 aligned Patented Nov. 23, 1971 axially with stationary contact 15 and the tube 27 is supported by a glass insulating ring 29 forming a top for enclosure 21. A cylindrically shaped insulating member 31 concentric with the internal surface of enclosure 21 insulates the periphery of element 13 from the enclosure 21. The rod 25 slides in the tube 27 to vary the force of contact 17 against the element 13.

In the circuit of the drawing the contacts 15 and 17 and a milliammeter 33 are connected in series across the output terminals 35 of a variable frequency generator 37, the generator 37 being connected to an A C source. The generator 37 is set to the resonant frequency of the element 13, and the rod 25 is adjusted to bring the contact 17 against one surface of element 13 until the maximum deflection of milliammeter 33 is obtained, whereupon rod 25 is permanently fastened (as by soldering) to tube 27.

In determining the adjustment of the movable contact 17 against the surface of the element 13 by varying the position of the rod 25 with the electrical circuit energized it will be noted that when the contact 17 makes no contact with the element 13 the circuit will be open, and no deflection of the milliammeter will occur. As soon as the contact 17 makes contact, however, there will be a deflection of some magnitude, thereafter the deflection of the milliammeter will increase to a maximum (indicating a point of resonance), and it is at this deflection of the milliammeter that the optimum condition of mounting the element 13 is attained.

While the invention has been explained and described with the aid of particular embodiments thereof, it will be understood that the invention is not limited thereby and that many modifications retaining and utilizing the spirit thereof without departing essentially therefrom will occur to those skilled in the art in applying the invention to specific operating environments and conditions. It is therefore contemplated by the appended claims to cover all such modifications as fall within the scope and spirit of the invention.

What is claimed is:

1. The method of mounting a piezoelectric ceramic element comprising the steps of applying a conductive coating to opposite surfaces of said element, placing the element between a pair of electrical contacts bearing upon the said coatings, connecting the contacts in series with a milliammeter and an alternating current generator, setting said generator to provide a voltage of a frequency corresponding to the operating frequency of said element, adjusting said contacts against the said surfaces until a maximum deflection of said milliammeter is obtained, and thereat fixing said contacts from further adjustment.

2. The method of claim 1 with the additional step of positioning the said contacts substantially in the centers of the said surfaces.

3. The method of mounting a piezoelectric ceramic element comprising the steps of placing the opposite surfaces of the element between a stationary contact and a movable contact resiliently attached to a plunger slidably positioned in a sleeve axially aligned with the stationary contact, connecting a milliammeter and a variable frequency generator in series with said contacts, setting said generator to provide a voltage of a frequency corresponding to the operating frequency of said elements, adjusting said movable contact against said elements surface, and fixing said plunger in said sleeve when a maximum deflection is obtained in said milliammeter.

4. A method of mounting a piezoelectric element comprising the steps of: placing opposite surfaces of said element between two contacts, at least one of which is movable; energizing said element with an electrical signal the frequency of which corresponds to the resonant frequency of said element; moving the movable contact to vary the pressure applied to said element while measuring the electrical response of the element, and securing the movable contact in that position at which said element exhibits maximum electrical response.

References Cited CHARLIE T. MOON, Primary Examiner 1 C. E. HALL, Assistant Examiner US. Cl. X. R. 

